Heat treatment

SOFT ANNEALING

Protect the steel and heat through to 780ºC (1440ºF).  Then cool in the furnace at 10ºC (20ºF) per hour to 650ºC (1200ºF), then freely in air.

STRESS-RELIEVING

After rough machining the tool should be heated through to 650ºC (1200ºF), holding time 2 hours.  Cool slowly to 500ºC (930ºF), then freely in air.

HARDENING

Preheating temperature : 600-850ºC (1110-1560ºF)
Austenitizing temperature : 1000-1050ºC (1830-1920ºF)
but usually : 1020-1030ºC (1870-1885ºF)

TEMPERING

Choose the tempering temperature according to the hardness required by reference to the temper-ing graph. Temper twice with intermediate cooling to room temperature. Lowest tempering temperature 180ºC (360ºF). Holding time at temperature minimum 2 hours.

Tempering graph

Note 1: Tempering at 250ºC (480ºF) is recommended for the best combination of toughness, hardness and corrosion resistance.

Note 2: Above curves are valid for small samples. Achieved hardness depends on mould size.

Note 3: A combination of high austenitizing temperature and low tempering temperature < 250ºC (480ºF) gives a high stress level in the mould and should be avoided.

For maximum hardness and best combination of toughness, corrosion resistance and dimension stability during use, following heat treatment cycle is recommended.

Subzero cooling is only required when demands on dimension stability during use are very high. Received hardness: 52 – 54 HRC.
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Polishing

POLMAX has extremely good polishability in the hardened and tempered condition.

A slightly different technique is needed when polishing corrosion resistant tool steel compared with conventional tool steel. The main principle is to use smaller steps at the fine-grinding/polishing stages and try to grind to as fine surface as possible before starting the polishing operation. It is also important to stop the polishing operation immediately the last scratch from the former grain size has been removed.

PRACTICAL HINTS

• Polishing should be carried out in dust-and draught-free places. Hard dust particles can easily    contaminate the abrasive and ruin an almost finished surface.

• Each polishing tool should be used for only one paste grade and kept in dust-proof container.

• The polishing tools gradually become “impreg-nated” and improve with use.

• Hands and workpiece should be cleaned carefully between each change of paste grade, the    work- piece with a grease solvent and the hands with soap.

• Paste should be applied to the polishing tool in manual polishing, while in machine polishing, the    paste should be applied to the workpiece.

• The finer the grain size, the less thinning liquid.

• Polishing pressure should be adjusted to the hardness of the polishing tool and the grade of the    paste. For the finest grain sizes, the pressure should only be the weight of the polishing tool.

• Heavy material removal requires hard polishing tools and coarse paste.

• Finish polishing of plastic moulds should be carried out in the release direction.

• Polishing should start in the corners, edges and fillets or the difficult parts of the mould.

• Be careful with sharp corners and edges, so they are not rounded off. Preferably use hard    polishing tools.

Cleanliness in every step of the polishing operation is of such great importance that it can not be over emphasized.
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Certificate

TO be sure POLMAX fulfil the high demands on cleanliness, which is required to obtain good polishability, each bar is individually tested and delivered with certificate.

Chemical composition, soft annealed hardness and microcleanliness are given in the certificate. Microcleanliness is rated according to ASTM E45 Method A, a well established standard method taking into consideration the amount of sulphides, oxides, silicates and globular inclusions.

Maximum inclusion level approved, according to ASTM E-45 Method A, Plate I – r

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Further Information

Please contact your local uddeholm office for further information on the selection, heat treatment, application and availability of Uddeholm tool steels.
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